Blender 2.8 rig not fully working on 2.79
Blender files created with newer versions of Blender should not be opened in older versions of Blender, especially with Blender 2.8 as a lot has changed. What I recommend is having more than one version of Blender installed and/or exporting models and using them in your scenes with newer or older versions of Blender (use DAE format, etc.).